It is well known to prepare network structures from embossed thermoplastic film and then sequentially stretching, biaxially or uniaxially. For example, U.S. Pat. No. 3,914,365 to Kim and Liu teaches a process of forming numerous parallel main ribs in one direction on one side of a sheet and a greater number of parallel tie ribs in a second direction on the other side of a sheet, the ribs forming a pattern of thick and thin areas in the sheet, then subsequently orienting the patterned film to open the sheet into the network structure. U.S. Pat. No. 3,488,415 to Patchell, et al, teaches a process for making a fabric from plastic material by providing both sides of a continuous sheet of plastic material with grooves which extend partly through the sheet, the grooves on one surface being arranged to cross the grooves on the other surface, the crossing points having only the reduced thickness of material which separates the bases of the grooves. The sheet is then biaxially stretched so that the thinned parts of the sheet split and form perforations at the slits.
Numerous other U.S. Pat. Nos. 4,075,379, 3,922,327, 4,207,375, 4,186,781 and 4,274,251 disclose improvements and/or modifications to the basic practice. The preferred orientation of lines or grooves is at 90.degree. to each other. In all cases, however, the embossed, patterned film is not porous until it is oriented. Furthermore, although not specifically stated in many of the patents, this process has been limited to high density polyethylene, polypropylene homopolymer, polypropylene copolymers, and polymer blends where aforementioned polymers are the major component. When these processes are implemented with soft, non-crystalline polymers, such as low density polyethylene apertures are not formed; a patterned closed film is produced.